1. Technical Field
The present invention generally relates to the field of data transmission protocols and, more particularly, to a method and apparatus for originating and receiving a unidirectional data communication for serial transmission in accordance with the present protocol, permitting variable sized data packets and variable data rates, thus enabling efficient reception at a receiver of many different types of data, the protocol operative within a layered network communications model.
2. Description of the Related Art
Toward the end of the 1970's, a network communications model evolved which has come to be known in the telecommunications art as the Open Systems Interconnect (OSI) model. This model operates at a plurality of seven layers including, for example, the applications layer relating to a particular application, the session layer for setting up a session, the presentation layer which facilitates the display of a message, the transport layer which facilitates transportation of messages, the network layer for facilitating connections in a network, the link layer and the physical layer. In this patent application, reference will be made to two functional layers analogous to the two lowest layers of the OSI model, the link layer and the physical layer. Any other functionality outside these two layers will be referred to herein as, for example, user circuits. By "user" is meant one who is involved in the design of a communications network including the design of message originating and receiving equipment. "Datagram" service as defined within the OSI model and as used in the present application relates to transmission of data from a transmitter to a receiver without any requirement for acknowledgement of receipt of a transmitted message by a receiver.
In the same time frame, a number of data transmission protocols began to evolve utilizing the OSI model as an overall framework including, for example, the so-called TAXI protocol. Developed by Advanced Micro Devices Corporation for data communications between chips of a chip set, TAXI may be used to implement or define a substantial potion of an OSI-like physical layer but TAXI neglects link layer functions. For example, TAXI does not specify inter-device control which may be needed in the physical layer. Moreover, the circuits for implementing TAXI fail to provide block error checking.
TAXI suffers from other disadvantages as well, the solutions to which are required in the new world of multimedia data communication. For example, with MPEG2 audio and video data compression, it is useful to pinpoint the beginning and length of the MPEG2 data packets. Moreover, in the new multimedia world, it is important to provide for variable length packets operating at variable rates. Perhaps most importantly, TAXI involves substantial costs to implement and yet would have to be bolstered in functionality to meet desired objectives. TAXI, because it does not go far enough in meeting the objectives of the present invention, expects a user to add functionality by means of their own protocol and powerful error detection.
Other known data protocols were considered for solving the problems of providing an efficient single wire or path link interface data communication protocol and discarded. The well known Ethernet protocol was considered and discarded because it does not permit operation at fast enough data rates and circuitry would be too expensive. The so-called FDDI protocol was considered and rejected as too expensive and because of excess bandwidth not being required. The inter-device RS-232 and RS-422 interface protocol were considered and discarded for being too slow, too short and requiring multiple conductors (not single wire).
Still other protocols were developed for other purposes, however, than to exchange variable data rate information such as digitized video (high data rate), audio, or slower speed data. Also, it became clear that a user may design the link layer and physical layer with anticipated noise sources in mind in such a way that transmission may occur relatively error free over a whole class of media. That class of media, for example, includes optical fiber, plastic fiber, coaxial cable, twisted pairs, solder runs on circuit boards, conductor runs, integrated circuit leads and so on, practically too numerous to detail here. Complex error detection and correction algorithms that might be required for, for example, satellite media, are not required for such ground-based media, including simple chip-to-chip data transmission contemplated by the TAXI protocol. More particularly, then, it became dear from a study of prior art protocols, there remains a requirement for a simple, efficient protocol permitting serial bit stream transmission of variable length packets at variable data rates over a single path.